[PBNTR-361] Implementing Dropdown form validation (#3507)

**What does this PR do?**
Implementing form validation for required Dropdown.

**Screenshots:** 
<img width="761" alt="image"
src="https://github.com/powerhome/playbook/assets/2573205/5265299d-a1fa-449b-928c-1e0c64eb2637">

**How to test?** 
1. Go to the Form kit doc
2. Scroll down to Validation doc


#### Checklist:
- [x] **LABELS** Add a label: `enhancement`, `bug`, `improvement`, `new
kit`, `deprecated`, or `breaking`. See [Changelog &
Labels](https://github.com/powerhome/playbook/wiki/Changelog-&-Labels)
for details.
- [x] **DEPLOY** I have added the `milano` label to show I'm ready for a
review.
- [ ] **TESTS** I have added test coverage to my code.

playbook/app/pb_kits/playbook/pb_dropdown/dropdown.html.erb

@@ -8,7 +8,9 @@
         <%= pb_rails("caption", props: {text: object.label, margin_bottom:"xs"}) %>
     <% end %>
     <div class="dropdown_wrapper<%= error_class %>" style="position: relative">
-        <input type="hidden" name="<%= object.name %>" id="dropdown-selected-option" value=""/>
+        <input type="hidden" name="<%= object.name %>" id="dropdown-selected-option" value="" />
+        <input id="dropdown-form-validation" name="<%= object.name %>_form_validation" value="" style="display: none" <%= object.required ? "required" : ""%> />
+
         <% if content.present? %>
             <%= content.presence %>
             <%= pb_rails("body", props: { status: "negative", text: object.error }) %>

playbook/app/pb_kits/playbook/pb_dropdown/dropdown.rb

@@ -8,6 +8,8 @@ class Dropdown < Playbook::KitBase
       prop :label, type: Playbook::Props::String
       prop :name, type: Playbook::Props::String
       prop :error, type: Playbook::Props::String
+      prop :required, type: Playbook::Props::Boolean,
+                      default: false
 
       def data
         Hash(prop(:data)).merge(pb_dropdown: true)

playbook/app/pb_kits/playbook/pb_dropdown/index.js

@@ -8,16 +8,22 @@ const DOWN_ARROW_SELECTOR = "#dropdown_open_icon";
 const UP_ARROW_SELECTOR = "#dropdown_close_icon";
 const OPTION_SELECTOR = "[data-dropdown-option-label]";
 const CUSTOM_DISPLAY_SELECTOR = "[data-dropdown-custom-trigger]";
+const INPUT_FORM_VALIDATION = "#dropdown-form-validation";
 
 export default class PbDropdown extends PbEnhancedElement {
   static get selector() {
     return DROPDOWN_SELECTOR;
   }
 
+  get target() {
+    return this.element.parentNode.querySelector(CONTAINER_SELECTOR);
+  }
+
   connect() {
     this.keyboardHandler = new PbDropdownKeyboard(this);
     this.bindEventListeners();
     this.updateArrowDisplay(false);
+    this.handleFormValidation();
   }
 
   bindEventListeners() {
@@ -38,9 +44,13 @@ export default class PbDropdown extends PbEnhancedElement {
   handleOptionClick(event) {
     const option = event.target.closest(OPTION_SELECTOR);
     const hiddenInput = this.element.querySelector("#dropdown-selected-option");
+    const inputFormValidation = this.element.querySelector(INPUT_FORM_VALIDATION);
+
     if (option) {
       const value = option.dataset.dropdownOptionLabel;
       hiddenInput.value = JSON.parse(value).id;
+      inputFormValidation.value = JSON.parse(value).id;
+      this.clearFormValidation(inputFormValidation);
       this.onOptionSelected(value, option);
     }
   }
@@ -103,10 +113,6 @@ export default class PbDropdown extends PbEnhancedElement {
     selectedOption.classList.add("pb_dropdown_option_selected");
   }
 
-  get target() {
-    return this.element.parentNode.querySelector(CONTAINER_SELECTOR);
-  }
-
   showElement(elem) {
     elem.classList.remove("close");
     elem.classList.add("open");
@@ -150,4 +156,27 @@ export default class PbDropdown extends PbEnhancedElement {
       upArrow.style.display = isOpen ? "inline-block" : "none";
     }
   }
+
+  handleFormValidation() {
+    const inputFormValidation = this.element.querySelector(INPUT_FORM_VALIDATION);
+
+    inputFormValidation.addEventListener("invalid", function (event) {
+      if (inputFormValidation.hasAttribute("required") && inputFormValidation.value === "") {
+        event.preventDefault();
+        inputFormValidation.closest(".dropdown_wrapper").classList.add("error");
+      }
+    }, true);
+  }
+
+  clearFormValidation(input) {
+    if (input.checkValidity()) {
+      const dropdownWrapperElement = input.closest(".dropdown_wrapper");
+      dropdownWrapperElement.classList.remove("error");
+
+      const errorLabelElement = dropdownWrapperElement.querySelector(".pb_body_kit_negative");
+      if (errorLabelElement) {
+        errorLabelElement.remove();
+      }
+    }
+  }
 }

playbook/app/pb_kits/playbook/pb_form/docs/_form_form_with_validate.html.erb

@@ -13,6 +13,14 @@
   ]
 %>
 
+<% 
+  example_dropdown_options = [
+    { label: 'United States', value: 'United States', id: 'us' },
+    { label: 'Canada', value: 'Canada', id: 'ca' },
+    { label: 'Pakistan', value: 'Pakistan', id: 'pk' },
+  ]
+%>
+
 <%= pb_form_with(scope: :example, method: :get, url: "", validate: true) do |form| %>
   <%= form.text_field :example_text_field, props: { label: true, required: true } %>
   <%= form.phone_number_field :example_phone_number_field, props: { label: "Example phone field" } %>
@@ -22,6 +30,7 @@
   <%= form.password_field :example_password_field, props: { label: true, required: true } %>
   <%= form.url_field :example_url_field, props: { label: true, required: true } %>
   <%= form.text_area :example_text_area, props: { label: true, required: true } %>
+  <%= form.dropdown_field :example_dropdown, props: { label: true, options: example_dropdown_options, required: true } %>
   <%= form.select :example_select, [ ["Yes", 1], ["No", 2] ], props: { label: true, blank_selection: "Select One...", required: true } %>
   <%= form.collection_select :example_collection_select, example_collection, :value, :name, props: { label: true, blank_selection: "Select One...", required: true } %>
   <%= form.check_box :example_checkbox, props: { text: "Example Checkbox", label: true, required: true } %>